Remote concentrator line circuit



Dec- 1, 1964 s. F. ABBOTT, JR., ETAL REMOTE CONCENTRATOR LINE CIRCUITFiled May 22. 1961 ATTORNEY United States Patent George l?. Abbott, ir.,Berkeley Heights, NJ., and Wiley Whitney, Columbus, Ohio, assignors toBeil Telephone Laboratories, incorporated, New Yorin NX., a corporationof New Yori:

Filed May 22, i961, Ser. No. MLS@ 17 Claims. (Ci. 179-43) This inventionrelates to telephone line concentrating systems and more particularly tocombined line and cutolf circuits for use at remote concentrators. Eachcornbinedline and cut-off circuit thus errnployecl` is associated with aremotely terminated substation in the line concentrator system.

Telephone line concentration has become the subject of considerableinterest in telephone switching technology. In part this is attributableto the savings in copper and other outside plant costs which result fromthe lack of necessity to directly connect each substation liney to thetelephone oiiice. Instead the lines are terminated at a remote unitsituated proximate to the `center of density of the area of subscribersto be served from which concentrator unit or switching unit entend anumber of trunks less in number than the number of lines. These trunksare connected to the telephone oiiice and are used on a shared basis bythe substation lines terminated at the conccntrator.

A particularly advantageous type of line concentrator is the so-calleduniversal type. 'The title is intended fto inclicate the universality ofits application, Le., it may be employed` in conjunction `with anyconventional type telephoneswiltching system. A singularly desirableaspect Patented Dee. l, 1964 tor unitin which the functions performed bythe tradiof the universal concentrator is that the telephone centralofiice existing or conventional equipment need not be substantiallymodified to render it compatible with concentrator operation. Y

Traditional central ottico terminated lines in telephone switchingsystems include aline relay or sensory device and a cut-olf relay fordivorcing the line relay from the line during a conversation connectionor the equivalent in other structures of the relays. The function of theline relay is in the nature of a rudimentary scanner. lWhen a substationgoes'of-hook, for example, the line relay con- `nected Ito the energizedline is operated to indicate this condition and to trigger theappropriate responsive apparatus in the central office to initiate aconnection to the calling substation line.V Since the sensory devicev orline relay is generally connected in shunt or in bridge with thesubstation line vit is obviously desirable, when a connection has beenextended to the line for conversation purposes, to eliminate theshunting effect of the line relay and thereby forestall the possibledeleterious effects on transmission occasioned by the bridgingimpedance.

In conventional switching systems the latter function is performed by acut-ofi relay which serves to isolate the winding'of the line relay fromthe line during the conversation connection.

In a universal line concentrator, and indeed, in any concentrator, vtheconventional line relay or sensory device at the central ofce is nolonger in direct metallic connection with the remotely terminatedsubstation line; As a result, facilities must be included at the remotelocation adapted to perform an analogous function. 1T he requirements atthe remote location are considerably more stringent however sincephysical size of the sensory and cutoif device is novva significantconsideration in view of the necessity to enclose, weatherproof and polemount the concentrator unit.

It is therefore an object of this invention to provide remote line andcut-olf facilities in a telephone line concentrator requiring minimalspace needs.

tional line and cut-off relays composite unit.

An additional consideration with respect to remote telephone lineconcentrators and a very material one is the tact that they areliterally remote from the central oflice. As a resuit power requirementsfor operation of the remote unit present challenging problems. Incontrast to the supply of energy to units at the central oiiice fromtradiare coalesced in a single tional power suppiy sources thetransmission of energy 4 to the remote unit may require the spanning ofseveral Y Under certain conditions the necessity t0' transmit power tothe remote unit may preempt the usage circuit miles.

ofV trunk connections between the remote unit and the central oiice.Since this type of transmission Vwas not required in direct linesystems, i.e., nonconcentrated systems, the necessity for Yprovidingconductors for power transmission is to that extent defeative of thevery purpose of line concentration which is to reduce the number ofconductors between the telephone subscribers and the central oiiice.

it is 'therefore an object of Vthis invention to provide remote line andcut-olf facilities for a line concentrator system in which the use ofcontinuous energy to operate the devices is not required.

Still another object of' this'invention is to provide sensory equipmentat a remote concentrator location Which may be energized by a minimalexpenditure of power and remainin the energized condition with nofurther expenditure of power. Y

ln certain universal concentrator systems the desirable feature ofdelayed disconnect is provided. A recent example of progressive effortsin this regard may be found in the concentrator system demonstrated in apatent of G. IF. Abbott, Ir., 2,692,555 of November 29, 1960. In thedelayed disconnect arrangement, when a subscriber has completed hisconversation the connection of the substation through the concentratoris nevertheless maintained. This procedure is desirable since itprecludes the necessityV of transmitting signaling information totheconcentrator appropriate to open the crosspoint at the remote switchingunit until the particular trunk to which the inacive substation isconnected` (which trunk has been marked as idle at the central oice)is'required to service in reducingthe signaling burden, in turngenerates a number of problems which stern from the fact that there isno permanent direct connection between each of the substation lines andthe central office. Thus an anomaly which results from concentratordelay disconnect practice in universal line concentrators is that theprimary line circuit, i.e., the conventional line and cut-off relay atthe centraloflice and the secondary line circuit, i.e., the improvedremote line and cut-olffacilities discussed above, may at times (andspecifically during a delayed trunk disconnect) reflect differentstates. Under these circumstances the primary line circuit wouldindicate accurately that the line connected to the trunk is idle andavailable for terminating or originating calls. The secondarylinecircuit or remote Aline circuit on the other hand, since the trunkremains connected to 'the substation, will be icompleteiy divorced vfromthe substation line by the cut-off facilities in the same manner asthough the substation were occupied with a conversation connection.

Reiiection on these circumstances is convincing ofthe necessity for thisprocedure.` In short, if a substation line in the idle condition butnevertheless connected to a assaut trunk to the central ofce as a resultof the delayed trunk disconnect procedure goes off-hook, the sensoryequipment in the remote unit will completely overlook this supervisoryindication since it is physically isolated by the cut-off uni-t from theline. Since the primary line circuit at the central office is connectedto the line, however, as indicated above, it will immediately react tothe ofi-hook condition to actuate the appropriate common controlapparatus in the central office to extend the call. Under theseconditions the concentrated line is processed effectually in the samemanner as though it were a direct connected line. This is understandablesince as a result of the delayed disconnect the substation line ineffect enjoys a direct connection over the idle trunk to the centraloffice.

It is thus apparent that either the sensory uni-t at the remote locationor the sensory unit at the central office location must have electricalaccess to the line to sense its supervisory condition. Recognizing thesefactors, the threat implicit in the use of remote line and cut-offequipment becomes evident. In short, if the line is divorced from theline relay or conventional sensory equipment at the central office andif the line is `also divorced from the remote sensory equipment or linerelay at the remote unit the customer is completely denied anyelectrical access to the oice. This follows since his line has becomewholly isolated and in effect he will be granted a dead line if hissubstation receiver is ltaken off-hook. Moreover, he will have no way ofcommunicating this fact to the'centraloflice.

It is therefore an object of this invention to provide remote line andcut-off facilities having a high degree of accuracy and reliability.

Still another object of this invention is to provide re' mote line andcut-oir" facilities which may be controlled with simplicity from aremote location to `refiect the same or different operating statesrelative to that of the line and cut-off facilities at the central ofcein accordance with the dictates of delay disconnect practice.

These and other objects and features of the invention are achieved in anillustrative embodiment in which the secondary line circuit comprisesthree reed switches or pairs of contacts of a type similar to thatdescribed in Patent 2,289,830 of W. B. Ellwood of July 14, 1942. Two ofthe contact sets are connected in bridge with the substation line andserve as the traditional cut-off contacts. The third contact set orswitch is normally open and reflects the supervisory condition of thesubstation to effect an alerting of central ofiice equipment byproviding a detectable condition to a line scanner at the remoteconcentrator. Physically the three switches are disposed in parallelaxial relationship. A permanent magnet Vis located in appropriaterelation with respect to two of the switches in order that theseswitches be magnetically latching in the closed condition and that they'remain indefinitely in the closed condition once operated theretowithout further additional power drain. The third switch for providingthe detectable condition reflecting the supervisory' state of thesubstation is not magnetically latching. The three switches areencompassed by two separate windings. A first of these windings isconnected to a concentrator network control and may be energized in onedirection or the other to operate or release the first and second pairsof contacts in accordance with the state of the substation. The secondwinding is connected in series with the contacts coupled to thesubstation line and is energizable in only one direction to operate thethird set of contacts. The three switches are physically similar to theEllwood switch described above although the first land second yswitchesmay be latched in the closed condition against the normal pull of thereeds by a permanent magnet.

The latching contacts are the contacts which conventionally appear onthe cut-off relay and the nonlatching set of contacts is the line relaycontacts.

In operation, when a subscriber substation goes offhook, current isapplied over the line tip and ring to the second winding which producesa flux suicient to close the third set of contacts and is in a directionto produce a still greater closing force for the normally closed firstand second contact sets which therefore remain closed.

As a result of the closure of the third set of contacts adetectablecondition is presented to a signaling network and scanner to initiatescanning of `all of the lines thereby to determine the identification ofthe off-hook line. Ultimately, when a trunk is connected to the callingline a signal is applied from a concentrator network control to thesecond winding to open all the latching contacts.

When the line is disconnected from the trunk the concentrator networkcontrol transmits an oppositely polarized pulse of lesser intensity thanthe previous pulse to the second winding to close the latching contacts.The first and second contacts remain magnetically latched in the closedposition while the third set remains in the open condition in view of amechanical bias which prevents closure by the smaller current.Alternatively, appropriate and conventional delay devices in the scannermay be used to ignore the short duration signal provided if the thirdset of contacts momentarily closes.

General Description These and other objects and features of theinvention may be more readily comprehended from an examination of thefollowing specification, appended claims and attached drawing, in which:

FIG. 1 shows a schematic diagram of the remote line and cut-ofifacilities in combination with a telephone concentrator system;

FIG. 2 shows an end elevation of the details of the switch structure ofFIG. 1; and

FIG. 3 shows relative flux direction for the switch structure.

Referring now to FIG. 1 the equipment includes a secondary line andcut-off circuit L00 having three sets of contacts. The cut-off contacts3 and 5 are normally closed when the substation is not connected to atrunk. These contacts 3 and 5 are connected in bridge with the tip andring conductors of the line respectively and in series with winding 11,which winding encompasses all three contact sets.

A further winding 13 also encompasses all three contact sets and isextended to the concentrator network control 31. Only that portion ofthe network control necessary for an understanding of the instantinvention is shown in FIG. l. For a comprehesive description of anetwork control suitable for use in conjunction with the instantinvention reference may be made to an application of G. F. Abbott, Ir.,Serial No. 111,571, filedon even date herewith.

The mark relay M and disconnect relay D are operated by suitableequipment in the concentrator network control as explained in theabove-referred-to application. For purposes of simplicity the operationof these relays is shown herein symbolically by the operation of manualswitches 4I and 42.

It is apparent that the operation of mark relay M as a result of theactuation of switch 41 drives a current throughvcoil 13 in a firstdirection and the subsequent operation of disconnect relay D drives apulse of current through the coil 13 in the opposite direction. Coil 13is wound in a manner which permits current of the first direction toopen the latching contacts and current of the second direction to closethe latching relay contacts as explained further herein.

In FIG. 1, line and cut-off circuit L00 is shown in detail. Line andcut-off circuit L139 is shown in outline form only for simplicityalthough it is understood to be identical in all respects to linecircuit L00. Moreover, al-

though only two line circuits are shown it is understood that anappropriate number may be grouped at the remote concentrator unit. Forexample, 14() line and cutot relays L through L13@ may be utilized toservice 140 substations S00 through S139.

The substations are connectable through concentrator network 2l totwenty trunks TKtl through Tl 1l9 which extend to the central oliice.The concentrator network is not shown in detail but may illustrativelyinclude appropriate crossbar or other switching .apparatus disclosed indetail in the above-referredto application of G. F. Abbott, lr,Signaling circuit 33 is adapted to transmit information relative to thersubstation supervisory conditions to and from the telephone centraloflice.

Scanner 14 is equipped to `examine the supervisory conditions of theline circuits L0@ through 1.139 by observing potential conditions atresistors Atl@ through Al. OR gate SR is adapted to transmit informationfrom any of the line circuits of the signaling circuit 33.

station S00 goes oit-hook. A circuit'may be traced as a result throughcoil lll and over switches 3 and 5 and the tip and Vring conductors ofthe substation line through the closed switchhook contacts of substationSith.

Current low through coil lll creates a flux in a direction to close allof the contacts. This flux aids'the latching ux provided by magnet '7 asshown in FIG. 3. Since switches 3 and 5 are already closed they remainin that condition. Switch 1, however, now closes as a result of theenergization of coil ll. Negative battery is applied through switch Ilto resistance 29 and the potential at terminal Attu experiences anegative excursion from ground potential to a more negative potential. Asignal is applied, as a result, through OR gate SR to the signalingcircuit 33 which transmits an appropriate signal to the central ,otliceindicating that a change in supervisory state has occurred. Equipment inthe central olicel (not shown in detail to preserve clarity) -isactuated and a signal is delivered from the central othce to thesignaling circuit to energize scanner 14 which ascertains theidentilication of the line requesting service.

When this is accomplished a signal is transmitted from the centralotiice through the signaling circuit to actuate the concentrator networkcontrol. This is done in coordination with the extension of a selectedtrunk, for example TKtl, through the concentrator network to substationStill. When the line is connected to the trunk a further signal istransmitted from the central otliceto aotuate the concentrator controland speciiically the mark relay M in the concentrator network control.Symbolically this is shown by the actuation of manual switch 4l. As aresult, contacts M in the network control are closed to deliver a burstof current .through coil l. This current is in a direction to cause theswitches 3 and 5 to open. Switches Sand 5 latch in the open conditionsince the inl'luence of permanent magnet 7 is not sufcient to reclosethem although sutlicient to retain them in the closed condition. Switchl continues in the closed condition (now under the influence of coil 13)until the burst of current is terminated. The current burst is designedto have a fast rise time to insure that contacts l remain closed as theyneutral llux position, is passed.

Since switches 3 and 5 are now in the open position it is apparent thatno further bridging impedance exists across the tip and ring conductors.The conversation connection may now continue indefinitely. Whensubscriber `Still completes his conversation and returns the receiver toits cradle reopening the switchhook contacts the substation rnaynevertheless remain .connected through the concentrator network 2l totrunk TK() under the delay disconnect procedure described supra. As aresult, the line circuit Ltlti remains completely divorced from the tipand ring conductors T and R and supervision is performed cut-olfequipment at the central office in the manner alluded to above.

lf it becomes necessary to Vutilize trunk Tltl, which has remainedconnected to substation Stitl, for another substation line, it is"essential to restore line circuit Lilli to its former sensory connectionto the tip and ring conductors of substation Suit. Under theseconditions if the trunk was disconnected Without restoring the linecircuit Lilli the subscriber at substation Still will thereafter befaced with a completely dead line since the tip and ring conductors areboth isolated from the remote line circuit at switches 3 and 5 and fromthe central oliice line circuit by the disconnection of the trunk TKl.'

As a result, a signal is transmitted from the central oice through thesignaling network to operate disconnect relay D which applies a burst ofcurrent through coil 13 in a direction opposite to that applied by thecontacts M.

This operation is shown symbolically by the actuation of DetailedDescription Having thus explained the significant aspects of theinvention in general outline a detailed description of the invention nowfollows. y

Referring to FlG. 1 the secondary line circuit is illustrated ascomprising three 4reed switches l, 3 and S. A permanent magnet 7 issupported in appropriate lixed relation with nonmagnetic support 9. Thenonmagnetic structure 9 may comprise any suitable material and includesthree cylindrical apertures for the insertion of switches Il, 3 and 5. Apermanent magnet 7 is inserted in an additional cavity. The permanentmagnet 7 is located within the envelope structure in closer contiguityto switches 3 and 5 than to switch l in order to provide a magnetic lluXdensity in the region of the switches 3 and 5 sufficiently in excess ofthe latching flux density, i.e., the flux required to maintain thoseswitches in the closed condition for au indelinite period. Furthermore,the envelope structure 9 is provided with a pair of peripheral orannular recesses forV the coils 1l and t3. Illustratively the switchesl, 3 and 5 are disposed in parallel axial relationship within coils 1liand 13. This physical disposition of the switches within the coils isshown clearlyin the end elevation of FIG. 2. It will be noted thatswitches 3 and 5 are l'atched in the closed condition and switch llwhich does not latch but must be held operated is in the open condition.

In View ofthe latched closed condition of switches 3 and 5 when the tipand ring conductors T and R of the substation line are not connected toany trunk through the concentrator network 2l, an electricallycontinuous path exists between switches 3 and 5 and the tip and ringconductors. This path is interrupted only at the switchhook contacts ofsubstation Silit. Thus the line circuit Ltltl is responsive tosupervisory conditions at the substation including a line oli-hookcondition to alert the central ofce with respect thereto. Whensubstation Seil goes oil-hook the switchhook contacts complete a pathfor the energization of .coil l over a circuit which may be traced fromnegative battery 25, coil ll, switchhook contacts 5, ring conductor R,substation Still, tip conductor T switch 3 to ground. Y

The energization of coil ll as a result of current llow therethroughproduces a flux which aids the flux existing through switches 3 and S asshown in FIG. 3 and moreover applies a sutiicient magnetomotive force tooperate the contacts of switch 1. The latter switch which serves as theline relay contacts extends a path from negative battery 26, resistance27, switch 1, resistance 29 to ground. Resistors 27 and 29 define avoltage dividing arrangement having a junction A60 at which the closureof switch 1 createst a voltage change. Prior to the operation oi' switch1 the voltage at resistor 29 is substantially ground potential. Whenswitch 1 is operated, some negative voltage appears at that junction asdetermined by the ratio of resistors 27 and 29. This negative Voltageappears at junction A as a suitable detectable condition for sampling byline scanner 14.

The resultant voltage at junction A00 is directed through the common ORgate SR as an alert signal by the remote signaling circuit 33 tosuitable central oliice equipment, not shown herein, but described indetail in the abovereferred-to application of Abbott. Appropriateequipment in the central oihce for processing an originating call isseized. Since coil 11 appears as a bridge across the tip and ringconductors T and R it is desirable that the secondary line circuit L00be isolated from the substation upon the connection of the substation toa trunk conductor, for example trunk conductor TKG.

In processing the originating call of substation S66 the central oflicewill ultimately extend a connection through concentrator network 21between the tip and ring conductors of substation S00 and an idle trunk,for example trunk TKO. The isolation of the secondary line circuit L00is effected by interrupting the path at switche-s 3 and 5. This in turninterrupts the energizing path of coil 11. The opening of the switches 3and 5 is under control of switching network control 31 which operatesmark relay M momentarily to deliver a burst of current through coil 13.The operation of mark relay M is through apparatus under control ofimpulses delivered from the central otlice over the signaling networkbut for purposes of simplicity is shown here as la manually operatedswitch 41. When switch 41 is momentarily operated, mark relay M operatesits appropriate contacts and a path may be traced from negative battery32, contacts of relay M, contacts of manual switch T0, coil 13, manualswitch T0, contacts of relay M to ground. The iiux produced by thecurrent through coil 13 is in a direction to oppose that through coil 11and the magnet 7 as shown in FIG. 3 but is insufficient to reclose thecontacts 3 and 5 despite the permanent magnet ux. Since contacts 3 and 5were closed previously they now open and remain in the open condition.Switch 1 remains operated under the influence of coil 13 until thecurrent through that coil subsides.

Individual relays T0 through T139 associated with circuits L00 throughL139 provide access to the network control 131. They are omitted forclarity and shown symbolically as manual switches. A comprehensivedescription of these relays is available in the above-referredto Abbottapplication.

In accordance with usual practice the concentrator network 21 isgoverned by concentrator network control 31 upon the operation of markrelay M to eiect a connection of the trunk TK() to the substation S60 atwhich the service request condition was initiated.

Moreover, the operation of relay M completes a path for the energizationof coil 13 in the manner described above. When switches 3 and 5 arelatched in the open condition substation S00 is isolated from the lineand cut-oil facilities L00 and a clean tip and ring (free of bridgingimpedances) to the central oice is provided.

This situation continues indefinitely until positive action is taken toreclose switches 3 and 5 thereby reconnecting the tip and ringconductors to line and cut-off circuit L00.

When the conversation connection is terminated and substation S0() goesolf-hook, switches 3 and 5 nevertheless remain open and the line remainsconnected through the concentrator network 21 to trunk TKO in view ofthe delayed disconnect feature of the instant concentrator system.

Under these vcircumstances substation S00 is in eiect granted a directconnection to the central oice over trunk TKO and the conventional lineand cut-oir facilities in the central oice (not shown) react to thesupervisory condition at substation S00 directly. The advantage isapparent in that no additional trunk selecting operation need beperformed and instead subscriber S00 is in direct communication with theappropriate common control equipment at the central oiiice necessary toextend the call.

In the event that the trunk circuit TKO is no longer in active use bysubstation S00 (substation S00 is onhook) and the trunk is needed toserve another call, it is necessary to release the connection inconcentrator network 21 between the tip and ring conductors ofsubstation S00 and trunk conductor TKO. From what has been explainedabove it is also vital to reconnect the subscriber substation S00 to hisremote line circuit L00 at this time. If such action is omitted theresult is that the subscriber is divorced from the central office by therelease of the crosspoints in concentrator network 21 and is alsodivorced from the line and cut-off circuit L00 at the switches 3 and 5.

Through apparatus associated with the release of the crosspoints in theconcentrator network 21 shown herein symbolically as a manually operateddisconnected relay D but explained in detail in the above-referred-toapplication of G. F. Abbott, Jr., coil 13 is energized, this time in adirection opposite to that traced previously. Thus when switch 42 isclosed and disconnect relay D is operated a path may be traced fromground, contacts of relay D, manual switch T0, coil 13, manual switchT0, resistance 37, contacts of relay D to negative battery 32. Thecurrent ilowing through coil 13 is in a direction tending to close allof the switches 1, 3 and 5. As indicated above, switch 1 is mechanicallybiased in the normally open condition and requires a predetermined fluxto produce a closure operation. The momentary closure of contacts D (inview of the impedance 37) produces a ux suflicient to close switches 3and 5 (as a result of the cumulative effect of the permanent magnet fluxand that due to coil 13) which remain in the latched closed conditionbut insuicient to close switch 1.

As a result, relay S00 is now reconnected to its line circuit Ltt) andan off-hook condition thereat will result in the energization of coil11, the closure of switch 1 and a sequence of operations identical tothat described above for an originating call.

It is understood that the above embodiments are merely exemplary andthat various modifications may be made without departing from the spiritand scope of the invention.

What is claimed is:

l. A telephone line concentrator system including a plurality of lines,a telephone central oiiice, a plurality of trunks extending from saidoice, a remote concentrator unit for connecting said lines to saidtrunks under control of said central oice, said unit comprising a remoteline and cut-olf circuit, said line circuit including combined cut-offswitching means and line switching means, magnetic means for latchingsaid cut-olf means in the closed condition indefinitely, means includingsaid cutoff switching means responsive to the initiation of a servicerequest condition on one of said lines for operating said line switchingmeans to indicate said service request condition on said line, and meansfor operating said cutoi switching means to an open condition on theconnection of one of said trunks to said line through said concentratorunit and for simultaneously releasing said line switching means.

2. A telephone concentrator system comprising a telephone centraloffice, a plurality of trunks extending from said office, a remotesubstation line, a remote concentrator network for connecting said lineto said trunks under control of said central office, combined remotesensory and cut-ott means connected to said substation visory signal tosaid concentrator network, means effective on the connection of saidline to a selected one of said trunks through said concentrator networkfor opening said first, second and third switching means, and meansresponsive to the operation of said first and second switching means tosaid open condition for isolating said line from said means forenergizing said third switching means.

3. An automatic telephone line concentrator system including a telephonecentral office, a plurality of trunks extending from said ofiice, aremote Vsubstation line, a remote switching network for connecting saidline to said trunks under control of said central ofiice, acombinedremote line andk cut-off circuit connected to said line and responsiveto supervisory conditions on said line, said line and cut-ofi circuitincluding first, second and third magnetic `reed switches, a first andsecond winding surrounding said reed switches, means responsive to aservice request condition on said line including said first and secondreed switches for energizing said first winding, said third switch beingoperative to close in response to the energization of said firstwinding,'means responsive to the closure of said third switch fordelivering a supervisory indication indicative of a service requestcondition to said central office, and means effective on the connectionof a selected idle trunk to said line by said switching network forenergizing said second winding to open said first, second and thirdswitches.

4. An automatic telephone line concentrator/system in accordance withclaim 3 including in addition means responsive to the disconnection ofsaid selected idle trunk from said substation line to energize saidsecond winding in the opposite direction thereby to reclose said firstand second switches.

5. An automatic telephone line concentrator system in accordance withclaim 4 including in addition permanent magnetic means disposedcontiguous to said first and second switch' means for maintaining saidfirst and second switches in the closed condition indefinitely withoutcontinuous power drain.

6. A remote line and cut-ofi circuit for a line concentrator systemcomprising first, second and third magnetic reed switches, first andsecond windings encompassing all of said switches, means for energizingsaid first winding over a path including said first and second switchesto close said third switch, and means for thereafter energizing saidsecond winding in a first direction to open said first and secondswitches.

7. A remote line and cut-ofi circuit in accordance with claim 6including in addition means for energizing said second winding in anopposite direction to reclose said first and second switches and tomaintain said third switch in the open condition.

8. A remote line and cut-off circuit in accordance with claim 7 whereinsaid means for energizing said second winding in said opposite directionincludes means for limiting the fiux developed by said second winding toa magnitude lower than the flux developed when said second winding isenergized in said first direction.

9. A remote line and cut-off circuit for a line concentrator systemcomprising first, second and third reed switch contacts, permanentmagnetic means disposed contiguous to said first and second switches formaintaining said switches in the closed condition indefinitely, a firstwinding and a second winding encompassing all of said switches, meansfor energizing said first winding over a path including said first andsecond switches to operate said third switch, means for energizing saidsecond winding` in a first direction to actuate said first and secondswitchesv to an open condition, and means for thereafter actuating saidsecond winding in a second direction to reclose said first and secondswitches and to maintain said third switch in the open condition.

10. A telephone line concentrator system including a telephone centralofiice, a plurality of trunks extending from said office, a remotesubstation line, remote concentrator means for connecting said line tosaid trunks under control of said central office, remote line and cutoffVmeans responsive to supervisory conditions on said line, said lineV andcut-ofi means including first, .second and third magnetic reed switches,first and second windings encompassing said switches, means responsiveto a service request conditionon said line including said first andsecond reed switches and said first winding for closing said third reedswitch, means connected to said third switch including Voltage dividermeans for delivering a change of potential indication indicative of aservice request condition to said central ofiice, means effective on theconnection of a selected idle trunk to said line for energizing saidvsecond winding in a first direction toreopen all of said switches, andmeans effective upon a disconnect condition at said substation and themaintenance of said connection between said line and said trunk formaintaining said first and second switches in kthe open condition.

111. An automatic telephone line concentrator system in accordance withclaim 10 including in addition means effective upon the disconnection ofsaid substation line from said trunk for energizing said second windingin an opposite direction to reclose said first and second switches andto maintain said third switch in the open condition.

12. A remote line and cut-off circuit for a line concentrator systemincluding first and second magnetic reed cut-ofi contacts, magnetic reedline contacts, a first and second winding encompassing said reedcontacts, permanent magnetic latching means for maintaining said firstand second cut-ofi contacts in the closed position indefinitely withoutpower drain, means including said cut-off contacts for energizing saidrst winding to actuate said line contacts, voltage divider impedancemeans responsive to the operation of said line contacts for generating apotential change indicative of a change in supervisory condition on saidline, means for energizing said second winding in a first direction at afirst current level to open said cut-off contacts and said linecontacts, andV means for energizing said second winding in an oppositedirection at a second current level for reclosing said cutoff contactsand maintaining said line contacts in the open condition.

13. A. remote line and' cut-off circuit for a line concentrator systemcomprising first and second magnetic reed switches, first 'and secondwindings magnetically coupled .to said switches, permanent magneticmeans disposed contiguous to said first switch for maintaining saidswitch in the closed position without power drain, means for energizingsaid first winding over a path including said first reed switch to closesaid second reed switch, said means including means for delivering apulse of current through said first winding in 4a direction .to producea fiux in aid of ythe ux produced by said permanent magnetic means, andmeans for thereafter energizing said second winding in a direction toproduce a flux in opposition to the flux produced by said first Windingand said permanent magnetic means to open said first magnetic reedswitch.

14. A remote line and cut-od circuit for a line concentnator system inaccordance with claim 13 including in addition means for energizing saidsecond winding in a direction to produce a flux in aid of said uXproduced by said permanent m-agnetic mean-s to reclose said first reedswitch.

15. A remote line and cut-off circuit for a line concentrator system inaccord-ance with claim 14 including in addition means for limiting saidflux produced by said second winding on operation to reclose said firstreed switch to a level less than said flux level produced by said secondwinding on `operation to open said first reed switch, said second fluxlevel being sufiicient when added to said flux produced by saidpermanent magnetic means to close said first reed switch butinsufficient to close said second reed switch.

16. An automatic telephone line concentrator system including a remotesubstation line, a central office, a plurr-ality of trunks extendingfrom said oliice, a concentrator network for connecting said line tosaid trunks, network control means for governing the operation of saidnetwork, a scanning circuit coupled to said centnal ofiice and -to saidnetwork control for detecting and indicating service conditions on saidline, remote line and cut-ofi means connected to said line includingfirst and second magnetic reed switches, first and second windingsmagnetically coupled to -said first and second -reed switches, meansresponsive to an off-hook condition on one of said lines for energizingsaid first Winding over a path including said first magnetic reed switchto operate said second reed switch, means responsive to the operation ofsaid second reed switch for delivering a service request signalto saidscanning circuit yand to said central ofiice, means in said networkcontrol means effective on the operation of said scanning circuit forgoverning said ooncentr-ator network to extend a connection from saidoff- -hook line .to .a selected idle trunk, and additional means in saidnetwork control means for momentarily energizing said second windingwith current in a first direction to open said first magnetic reedswitch thereby deenergizing said first winding and releasing said secondmagnetic reed switch.

17. An automatic telephone line concentrator system in accordance withclaim 16 including in addition means in said network control means forgoverning said concentrator network -to disestablish said connectionbetween said line and said selected trunk and for delivering a pulse ofcurrent in an opposite direction through said second winding, said pulseof current being of a lesser magnitude than said current of said firstdirection and adapted to produce a flux suflicien-t to reclose saidfirst reed switch but insufficient to reclose said second reed switch.

References Cited in the file of this patent UNITED STATES PATENTS2,187,115 Elwood et al Jan. 16, 1940 3,022,382 Ewin Feb. 20, 19623,030,451 Jacobson Apr. 17, 1962

3. AN AUTOMATIC TELEPHONE LINE CONCENTRATOR SYSTEM INCLUDING A TELEPHONECENTRAL OFFICE, A PLURALITY OF TRUNKS EXTENDING FROM SAID OFFICE, AREMOTE SUBSTATION LINE, A REMOTE SWITCHING NETWORK FOR CONNECTING SAIDLINE TO SAID TRUNKS UNDER CONTROL OF SAID CENTRAL OFFICE, AN COMBINEDREMOTE LINE AND CUT-OFF CIRCUIT CONNECTED TO SAID LINE AND RESPONSIVE TOSUPERVISORY CONDITIONS ON SAID LINE, SAID LINE AND CUT-OFF CIRCUITINCLUDING FIRST, SECOND AND THIRD MAGNETIC REED SWITCHES, A FIRST ANDSECOND WINDING SURROUNDING SAID REED SWITCHES, MEANS RESPONSIVE TO ASERVICE REQUEST CONDITION ON SAID LINE INCLUDING SAID FIRST AND SECONDREED SWITCHES FOR ENERGIZING SAID FIRST WINDING, SAID THIRD SWITCH BEINGOPERATIVE TO CLOSE IN RESPONSE TO THE ENERGIZATION OF SAID FIRSTWINDING, MEANS RESPONSIVE TO THE CLOSURE OF SAID THIRD SWITCH FORDELIVERING A SUPERVISORY INDICATION INDICATIVE OF A SERVICE REQUESTCONDITION TO SAID CENTRAL OFFICE, AND MEANS EFFECTIVE ON THE CONNECTIONOF A SELECTED IDLE TRUNK TO SAID LINE BY SAID SWITCHING NETWORK FORENERGIZING SAID SECOND WINDING TO OPEN SAID FIRST, SECOND AND THIRDSWITCHES.